No matter how eager you are to get started with your new extension, it is a huge undertaking and it does require a little thought and planning to get right. The better you plan the more effective the end result will be. Before you start excitedly choosing soft furnishings and paint colours, there are so many other important things to think about first. In this guide we will walk you through some of the key considerations that you should factor in when planning an extension project.

How you use your home

One of the first things that a good building firm will do before you even start the build process is to find out the purpose of the extension. Understanding what you want to use the new space for will greatly help with the planning process. Usually extensions are undertaken for the following reasons:

  • Maximise the available space
  • Accommodate a growing family
  • Increase the value of the property
  • Create some much needed space in the short term before moving to a new home once finances and circumstances change
  • Alterations or an upgrade by adding a new open plan kitchen diner, a home office or adding on another bedroom

Cost of an extension

One of the most significant factors to think about when it comes to your extension project is the budget. It’s important to be realistic when thinking about your extension. Setting a budget and communicating this with your builder can not only save design time, but also expectations on the project – and whether or not they are realistic. Also factor in VAT if your builder charges this because the VAT can soon add up. The overall cost of an extension depending on what you want is between £1000 and £1250 per square meter for building. However, this is just a guide and the actual cost will vary depending on how complex your project is and the finish that you want to achieve.


When an extension is properly planned and constructed it can take many months to get from the design and planning phase through to completion. Usually it takes 4-6 weeks for the survey and design, 8-10 weeks to process any planning applications, 4-6 weeks to create working drawings and submit these for approval to building control, 2-4 weeks to tender a project and then the build time. You may start to navigate through the planning process, and you are notified that something in the design must be changed and this can cause delays to the process for weeks or sometimes months until an alternative is considered and submitted. Good building firms and architects are likely to foresee any issues in the process and they will be read to address them if they do. If you want to start your project in the summer, it is recommended that you start the planning process long before this time and you get your builder in place so they can start when you want them to.

Another factor to consider in terms of timescale is whether the work needs to be completed in stages. This may be important if you are living in your home through the construction process. Other things that you need to think about which could delay progress include the weather and availability of resources. Certain materials may need to be ordered well in advance so communicating with your building firm is key.

Extension services

When you build a new extension, you will need various ‘services’ to make the extension part of your home. By ‘services’ this means gas, electricity, water and drainage. If the extension is going to need any of these things, will you need to move service pipes, electricity supply or gas meters. Drainage is important too. Are there any manhole covers or other drainage systems on the site of where you intend to build? Sometimes drainage is adopted by the local water company particularly when it’s shared between properties; if you do need to build over an adopted sewer you will need to obtain a build over sewer application.

Neighbouring Properties

There are several questions to ask to determine whether your extension will affect any neighbouring properties:

  • Do you share a party wall?
  • Could they potentially complain over a right to light?
  • Are there any trees on site that may need to be removed?
  • Who owns the boundary fence, wall or hedge?
  • Would your extension cause any problems overshadowing their garden?

If your extension is subject to planning permission, there is a chance that neighbours may object. If you haven’t already, speak to your neighbours and discuss the extension that you intend to build on your house.


Everyone is concerned about running costs associated with our homes. Your existing house may have single glazing in places, poor ventilation, condensation or have poor loft insulation. While you are extending your home, this could be an ideal time to increase its overall energy efficiency. Older properties in particular would benefit the most from some energy efficient upgrades including:

  • Cavity wall insulation
  • Loft insulation
  • Windows and Doors that are more energy efficient
  • Upgrades to your boiler and radiators – An important consideration. Will your existing heating system be able to cope with the additional radiators used in the extension?
  • Solar panels
  • Air source heat pumps or ground source pumps

There is certainly a lot to think about when it comes to building an extension but if you have the right team on board, there is every possibility that the new addition to your home will be a huge success.